How Much to Turn Around in a NCP Car Park

Here is a simple maths problem...

It costs £25 to park for up to 4 hours in an NCP car park.
You park for 3 hours and 20 minutes.
You put your ticket in the machine and pay £25.

You take a wrong turn leaving in the car park and spend a few minutes turning around.

How much additional do you have to pay to get out of  the car park?